Craig Nelson and Wayne Maumbe will be presenting. Craig is working with Professor David Hansen, and Wayne is working with Professor Sandra Burkett.
Craig Nelson will discuss “Can Amino-Acid-Functionalized Naphthalenediimide Nanotubes Function as Ion-Channels?” Since their discovery, self-assembling organic nanotubes have attracted considerable attention for their industrial, ecological and biological potential. Work done by the Ghadiri group at the Scripps Research Institute in La Jolla, CA, has been a major contributor to this field, and has illuminated the biocidal potential of nanotubes formed from cyclic D,L α-peptides. Biocidal activity stems from the nanotubes’ capacity to pierce the cell membrane and form ion-channels, inducing cell death through the rapid breakdown of critical concentration gradients. My research project intends to expand upon this previous work, specifically by studying amino-acid-functionalized naphthalenediimide (NDI) derivatives, which the Sanders group at Cambridge University has demonstrated form nanotubes in solution. Using synthetic unilamellar vesicles as a model, membrane insertion and ion-channel formation by NDI nanotubes will be assayed through the use of the pH-dependent dye carboxyflourescein and fluorescence spectroscopy. If membrane insertion is confirmed, successive experiments will compare the activity of the NDI system to naturally occurring channel formers, including the antibiotic gramacidin.
Wayne Maumbe will discuss “NMR Investigations of Magnesium Organosilicate Clay Layers”. Clays are inorganic solids with crystalline, layered structures. Organically functionalized derivatives of the magnesium silicate clay talc have been used in the Burkett lab to synthesize polymer–clay nanocomposites with a brush-like structure. At the macroscopic level, these materials resemble the component polymer, including being soluble in organic solvents. In order to better understand the molecular-level properties of these nanocomposites, a derivative of talc, magnesium hexadecylsilicate, is used as a model system. This organoclay has a layered brush-like structure, with hexadecyl chains end-tethered to a talc core. The clay exfoliates into individual brush-like layers in solvents such as chloroform, THF, toluene, and 1,1,2,2-tetrachloroethane, making it possible to obtain solution 1H NMR and 13C NMR spectra. 1H NMR provides evidence of restricted alkyl chain mobility, and 13C NMR provides information about chain conformation. To further study mobility, the spacing between the hexadecyl chains is increased by incorporating propyl groups into the clay. Magnesium mixed-organosilicate clays were synthesized with 75%, 50%, and 25% hexadecyl groups, and magnesium propylsilicate was also prepared. NMR studies of alkyl chain mobility and conformation include 1H peak linewidth analysis and integration, 1H T1 and T2 relaxation time measurements, and 13C chemical shift analysis. The alkyl chain distributions within the mixed clays will be studied by investigating through-bond and through-space interactions using 1H 2D COSY and NOESY NMR experiments.